User's Manual

6 Serial Interfaces

6.1 UART Interface

WT32 Universal Asynchronous Receiver Transmitter (UART) interface provides a simple mechanism for

communicating with other serial devices using the RS232 standard. The UART interface of WT32 uses

voltage levels from 0 to VDD_IO and thus an external transceiver IC is required to meet the voltage

level specifications of RS232.

Figure 6: WT32 UART interface

Four signals are used to implement the UART function, as shown in Figure 7Figure 6. When WT32 is

connected to another digital device, UART_RX and UART_TX transfer data between the two devices.

The remaining two signals, UART_CTS and UART_RTS, can be used to implement RS232 hardware

flow control where both are active low indicators. DTR, DSR and DCD signals can be implemented by

using PIO terminals of WT32. All UART connections are implemented by using CMOS technology and

have signaling levels of 0V and VDD_IO.

In order to communicate with the UART at its maximum data rate using a standard PC, an accelerated

serial port adapter card is required for the PC.

Parameter

Possible values

Baud rate

Minimum

1200 baud (≤2%Error)

9600 baud (≤1%Error)

Maximum

3.0Mbaud (≤1%Error)

Flow control

RTS/CTS, none

Parity

None, Odd, Even

Number of stop bits

1 or 2

Bits per channel

Table 10: Possible UART settings

The UART interface is capable of resetting WT32 upon reception of a break signal. A Break is identified

by a continuous logic low (0V) on the UART_RX terminal, as shown in Figure 7. If tBRK is longer than

the value, defined by the PS Key PSKEY_HOST_IO_UART_RESET_TIMEOUT, (0x1a4), a reset will

occur. This feature allows a host to initialize the system to a known state. Also, WT32 can emit a Break

character that may be used to wake the Host.

Since UART_RX terminal includes a weak internal pull-down, it cannot be left open unless disabling

UART interface using PS_KEY settings. If UART is not disabled, a pull-up resistor has to be connected

to UART_RX. The UART interface requires an external RS232 transceiver, which usually includes the

required pull-up.

UART_TX

UART_RX

UART_RTS

UART_CTS

WT32